1. Field of Invention
The present invention relates to a Micro-Electro-Mechanical System (MEMS) integrated chip, and a method for making the MEMS integrated chip.
2. Description of Related Art
MEMS devices are used in a wide variety of products such as micro-acoustical sensor, gyro-sensor, accelerometer, etc. A MEMS chip typically includes a MEMS device and a microelectronic device, integrated together. In one prior art, the MEMS device and the microelectronic device are placed on a same surface of a wafer. By way of example, FIG. 1 is a planar view showing an integrated chip including a MEMS device area 100 and a microelectronic device (e.g., a CMOS device) area 200. The MEMS device area 100 is surrounded by a guard ring 120 to protect the microelectronic device area 200 from damages due to the etching process in making the MEMS device.
Referring to FIG. 2, which is a cross-section view along the line A-A of FIG. 1. During the manufacturing process of the microelectronic device and the MEMS device, multiple dielectric layers 19 are deposited on a substrate 11 (wherein interfaces between layers are not shown). In this prior art, a movable MEMS device (not shown) is formed in the MEMS device area by etching the dielectric layer 19 in the MEMS device area 100; thus, a space 10 is left in the MEMS device area 100. As mentioned earlier, it should be careful not to damage the microelectronic device area 200 during etching the dielectric layer 19. Therefore, a guard ring 120 is provided, which includes a polysilicon layer 12, metal layers 14, 15, 16, 17 and 18, and the multiple dielectric layers 19. The number of the metal layers may be determined according to the requirement for interconnection of the microelectronic device and the design of the MEMS device.
In order to functionally connect the microelectronic device and the MEMS device on the same surface of the wafer, an electrical connection must be provided therebetween. The foregoing prior art achieves this connection by means of one or more metal layers, such as the second metal layer 16 shown in FIG. 2. However, such one or more metal layers must go through the guard ring 120, and the positions where they go through the guard ring 120 can not form a tightly closed structure with other portions of the guard ring 120 (i.e. the contact layer 14, and the first metal layer 15 in the drawing); otherwise, it causes short circuit. Therefore, in this prior art, the microelectronic device area 200 can not be completely prevented from being damaged in the etching process for forming the MEMS device.
In addition, in the prior art, the geometry consumes more area space and is disadvantageous to area shrinkage because it places the MEMS device and the microelectronic device on the same surface.
Accordingly, it is highly desired to provide a structure which functionally connects the MEMS device and the microelectronic device but still completely protects the microelectronic device area, and furthermore reduces the required chip area.